This invention relates to a gas distributing system, and more particularly, to a gas sparger for providing a desired spray pattern of a gas, the gas sparger of the present invention being utilized in a muffle furnace for firing multilayered ceramic carriers (or substrates) used to mount and interconnect a plurality of integrated circuit chips.
The currently exists furnaces for firing of precious metals, such as gold. The firing of precious metals can be accomplished in the presence of air (i.e., oxygen) since the precious metals will not oxidize, and atmosphere contaminants will not interfere with the firing of the precious metal. Therefore, the gas distribution system (or gas sparger, or more simply sparger) is of relative importance in controlling the atmosphere within these furnaces. No furnace presently exists which has been designed specifically for the firing of thick film pastes of a non-precious metal, in which the film paste of a non-precious metal can also include an organic vehicle material. (The non-precious metal referred to herein being copper, which is used in the manufacturing processes of a multilayered substrate for mounting electronic circuit components.)
The industry has tried to use the aforementioned precious metal furnaces for firing of thick film paste of a non-precious metal with little success. Many problems have been encountered; specifically, there is an insufficient exhaust system to evacuate the gases from the burnout zone. Also, there exists an insufficient fresh gas distribution system in the burnout and firing zones, the gas distribution system in the burnout zone being the subject matter of the present invention. These problems exist because the organic vehicle contained in the film paste generates substantial amounts of combustion products which needs to be burned off and evacuated. The existing furnaces have two exhaust stacks, one placed in the front end of the burnout zone immediately past the entrance curtains (which is essentially a cold zone) and the other located directly above the barrier separating the burnout zone from the firing zone. In existing furnaces, displacement of the burnout exhaust causes the burn off gas to flow against the substrate movement causing reduced microatmospheres above the substrates causing incomplete burnout and which results in problems such as reduced solderability and loss of adhesion, the substrate(s) being placed on a chain belt which moves through the furnace.
The firing of a thick film paste of a non-precious metal needs to be accomplished in an inert atmosphere; however, oxygen must be used to burn off the organic vehicle otherwise the organic material carbonizes which can cause short circuits in the substrate. Thus, a mixture of nitrogen and oxygen is injected into the burnout zone of the furnace by the gas distribution system of the present invention thereby providing a clean (i.e, free of contaminants) atmosphere, but a careful balance needs to exist to insure the non-precious metal (copper) is not oxidized. Thus, there exists a need for a gas distribution system for use in furnace specifically designed for the firing of a thick film paste of a non-precious metal, wherein the film paste can also include an organic vehicle material.